From 0d6526f82c3cdefcca47f73f5fc08dc6f335eac6 Mon Sep 17 00:00:00 2001 From: Tim Chen Date: Mon, 21 Sep 2026 17:37:22 -0700 Subject: sched/cache: Keep nr_pref_llc_running in the runnable domain, to fix LLC mis-scheduling bug alb_break_llc() decides whether to break LLC preference during active load balance. It does so by testing that every runnable fair task on the source rq prefers its LLC: env->src_rq->nr_pref_llc_running == env->src_rq->cfs.h_nr_runnable But the two counters cover different sets. nr_pref_llc_running is updated in account_llc_enqueue()/account_llc_dequeue(), next to cfs_rq->nr_queued, so it follows queued tasks. h_nr_runnable is updated in set_delayed()/ clear_delayed() and drops delay-dequeued tasks. So under DELAY_DEQUEUE, a preferring task that goes to sleep stays counted in nr_pref_llc_running while h_nr_runnable falls. The equality then breaks, alb_break_llc() returns false, and active balance is free to pull a task off its preferred LLC. Active balance only moves runnable tasks, and this is the only LLC check it consults: once the stopper runs, LBF_ACTIVE_LB skips the per-task test in can_migrate_task(). The runnable set is the one we want. Fix it on the counter side. A task should be counted in nr_pref_llc_running exactly while it is both queued on its preferred LLC (pref_llc_queued) and runnable (!sched_delayed). Define that membership once in task_pref_llc_runnable(), and adjust the counter only through pref_llc_running_inc()/pref_llc_running_dec() from the four sites that change either input: account_llc_enqueue(), account_llc_dequeue(), set_delayed() and clear_delayed(). Gating every update on the same predicate keeps the delay, wake and dequeue paths from double-counting or underflowing; see the comments at those sites for the ordering. nr_llc_running and sd->llc_counts are not touched and stay on queued semantics. Fixes: 714059f79ff0 ("sched/cache: Handle moving single tasks to/from their preferred LLC") Closes: https://lore.kernel.org/lkml/20260827135000.735138-1-zhanxusheng@xiaomi.com/ Reported-by: Zhan Xusheng Suggested-by: Chen Yu Signed-off-by: Tim Chen Signed-off-by: Peter Zijlstra (Intel) Signed-off-by: Ingo Molnar Reviewed-by: Kayra Cizmeci Cc: # v7.2.x Link: https://patch.msgid.link/06af61afedac32e6477f57feb4d658f6c411c3af.1790035273.git.tim.c.chen@linux.intel.com --- net/rxrpc/call_state.c | 69 ++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 69 insertions(+) create mode 100644 net/rxrpc/call_state.c (limited to 'net/rxrpc/call_state.c') diff --git a/net/rxrpc/call_state.c b/net/rxrpc/call_state.c new file mode 100644 index 000000000..6afb54373 --- /dev/null +++ b/net/rxrpc/call_state.c @@ -0,0 +1,69 @@ +// SPDX-License-Identifier: GPL-2.0-or-later +/* Call state changing functions. + * + * Copyright (C) 2022 Red Hat, Inc. All Rights Reserved. + * Written by David Howells (dhowells@redhat.com) + */ + +#include "ar-internal.h" + +/* + * Transition a call to the complete state. + */ +bool rxrpc_set_call_completion(struct rxrpc_call *call, + enum rxrpc_call_completion compl, + u32 abort_code, + int error) +{ + if (__rxrpc_call_state(call) == RXRPC_CALL_COMPLETE) + return false; + + call->abort_code = abort_code; + call->error = error; + call->completion = compl; + /* Allow reader of completion state to operate locklessly */ + rxrpc_set_call_state(call, RXRPC_CALL_COMPLETE); + trace_rxrpc_call_complete(call); + wake_up(&call->waitq); + rxrpc_notify_socket(call); + return true; +} + +/* + * Record that a call successfully completed. + */ +bool rxrpc_call_completed(struct rxrpc_call *call) +{ + return rxrpc_set_call_completion(call, RXRPC_CALL_SUCCEEDED, 0, 0); +} + +/* + * Record that a call is locally aborted. + */ +bool rxrpc_abort_call(struct rxrpc_call *call, rxrpc_seq_t seq, + u32 abort_code, int error, enum rxrpc_abort_reason why) +{ + trace_rxrpc_abort(call->debug_id, why, call->cid, call->call_id, seq, + abort_code, error); + if (!rxrpc_set_call_completion(call, RXRPC_CALL_LOCALLY_ABORTED, + abort_code, error)) + return false; + if (test_bit(RXRPC_CALL_EXPOSED, &call->flags)) + rxrpc_send_abort_packet(call); + return true; +} + +/* + * Record that a call errored out before even getting off the ground, thereby + * setting the state to allow it to be destroyed. + */ +void rxrpc_prefail_call(struct rxrpc_call *call, enum rxrpc_call_completion compl, + int error) +{ + call->abort_code = RX_CALL_DEAD; + call->error = error; + call->completion = compl; + call->_state = RXRPC_CALL_COMPLETE; + trace_rxrpc_call_complete(call); + WARN_ON_ONCE(__test_and_set_bit(RXRPC_CALL_RELEASED, &call->flags)); +} -- cgit v1.3.1